DE102012214412B3 - Absorber pipe for parabolic trough collector in solar thermal parabolic trough power plant, has shielding device including ring disk-like section, which covers connecting region of connecting element and inner end of compensation device - Google Patents

Abstract

The pipe (1) has an annular space section (7) of an inner annular space (6) formed between a glass-metal transition element (10) and a connecting element (30). The connecting element and an expansion compensation device (20) i.e. bellow, include a circular ring-like front surface in an axial top view. A shielding device (50) is arranged at ends (1a, 1b) of the pipe, and includes a ring disk-like section (52), which is arranged at a distance before the front surface in an axial direction and covers a connecting region (100) of the connecting element and an inner end of the compensation device.

Description

The invention relates to an absorber tube according to the preamble of claim 1.

The DE 10 231 467 B4 describes such an absorber tube, which is used in particular for parabolic trough collectors in solar power plants. The absorber tube has a central metal tube and a glass tube surrounding the central metal tube. The glass tube is provided at both ends with a glass metal transition element, on each of which a strain compensation device or a connecting element engages. The expansion compensation device is at least partially disposed in the annular space between the metal tube and the glass transition element.

The connecting element may extend in the annular space between the expansion compensating device and the metal tube, whereby in a conical configuration of the connecting element flat incident radiation and the radiation of the metal tube is reflected back to the metal tube.

The connection element can also extend in the annular space between the expansion compensation device and the glass tube and in this case is connected to the glass metal transition element. The connecting element has a fastening element in the form of an annular disc, with which the connecting element is attached to the expansion compensation device, which may comprise a bellows.

From the DE 60 223 711 T2 An absorber pipe is known in which the glass metal transition element and the expansion compensation device are arranged in the form of a bellows in the axial direction one behind the other. On the outside, a first shield element which shields the bellows, and a second shield element are provided, which shields the glass metal transition element from incident radiation. In addition, an internal radiation shield is arranged in the annular space between the cladding tube and metal tube in the region of the glass metal transition element. The internal radiation shield is hung with retaining arms in the bellows.

A disadvantage of this arrangement with bellows with glass metal transition element is the relatively large length, which leads to a reduction of the free aperture and thus the efficiency.

By one of the two outer shield elements, the glass metal transition element is initially protected from direct irradiation from the outside. The inner, an L-shaped cross-section radiation shield has only support arms in the region of the glass metal transition element, so that flat incident and reflected radiation from the metal tube in the area between the support arms can impinge on the glass metal transition element. Only part of this radiation is trapped by the inner radiation shield.

This construction has the further disadvantage that it itself absorbs radiation and thereby heats up. The inner radiation shield is thermally coupled to the bellows only insufficiently via the support arms, so that the portion of the radiation that is absorbed by the ring component must largely be released again by radiation. A significant portion of the heat radiation, in turn, hits the glass-to-metal transition element. As a result, the glass transition metal element undergoes a secondary heat input by radiation from the heated radiation shield.

Either DE10231467B4 as well as DE60223711T2 reveal an external protection of the glass-to-metal transition and the expansion compensation device. This external protection is usually mounted in the power plant after installation of the receiver. Reflector plates are mounted in the field after the receivers have been welded together.

A disadvantage here is that the glass-to-metal transition during transport and during installation is unprotected and can be easily damaged. Scratches in the cladding tube may occur during the assembly process, with scratches in the vicinity of the glass-to-metal transition element being particularly critical, leading to weakening of the absorber tube and later glass breakage during operation.

The object of the invention is, starting from the prior art according to the DE 10 231 467 B4 To further increase the life of the absorber tube.

This object is achieved with the features of claim 1.

It is provided that at least one shielding device is arranged at least at one end of the absorber tube in the annular space, which has a first annular disc-shaped portion which is arranged in the axial direction spaced from the end face and covers at least the connection region of the connecting element and the inner end of the expansion compensation device.

The end face and the connection area are in connection with the 1b explained.

The first annular portion has the advantage that it not only the Connection region of the expansion compensation device and the connection element but also protects the glass metal transition element from radiation reflected from the metal tube.

It has been found that the glass transition metal element and the expansion compensation device with respect to the service life of the absorber tube are critical components.

Although the radiation reflected by the metal tube or radiated radiation is partly kept away from the glass transition metal element by the expansion compensation device, since the expansion compensation device is disposed below the glass metal transition element, but this has the disadvantage that the radiation then impinges on the expansion compensation device and permanently the material of the Strain compensation device, in particular also the area where the expansion compensation device is connected to the connection element is damaged. There may under certain circumstances come to leaks at the contact points, so that then in the annulus, the required vacuum is lost or the inert gas filling in the annulus is contaminated by air ingress. By means of the shielding this damage is avoided. It has been shown that with the first annular disk-shaped section of the shielding device in the annular space of the absorber pipe, the service life of the absorber pipe can be effectively increased.

On the size of the surface of the first annular disc-shaped portion, the amount of radiation to be shielded can be adjusted specifically.

The first annular disk-shaped section preferably covers at least 50% of the end face, in particular preferably the entire end face.

The radiant energy impinging on the first annular portion causes heating of the first annular portion and is distributed by conduction in the surface of the shield, thereby lowering the temperature level. Due to the preferably smooth surface, most of the radiation is reflected directly to the outside or to the metal tube, while in the prior art, a larger part of the radiation is absorbed in the Belgschlaufen. The absorbed part of the radiation is distributed by heat conduction throughout the shielding means, whereby a uniform temperature level is achieved throughout the shielding means. The shielding device is preferably connected to a metallic component of the absorber tube, with the exception of the metal tube, so that the heat can also be dissipated. This will be explained in detail.

The first annular disk-shaped section can be arranged perpendicular to the longitudinal axis L. However, it is particularly preferred that the first annular disc-shaped section is arranged inclined with respect to a vertical S on the longitudinal axis L of the absorber tube by an angle α ≥ 0. The first annular disk-shaped section is preferably arranged inclined in such a way that a radially outer edge projects axially further into the annular space than a radially inner edge of the first annular disk-shaped section.

This embodiment has the advantage that a large part of the obliquely incident rays does not strike the shielding device, where it partially leads to the unusable heating of the same, but occurs directly on the metal tube and is converted there into usable heat. The inclination of the first annular portion enlarges the effective area of the absorber tube as compared to a non-inclined end portion.

Preferably, the angle α is in the range of 0 ° -30 °. This range is preferred because the solar radiation occurs particularly frequently at an angle of approximately 20 ° in the annual average at usual sites for solar thermal parabolic trough power plants.

At an angle> 30 °, the radially outer edge of the shielding device would be displaced axially towards the middle of the pipe, thus covering a part of the metal pipe, whereby the effective length of the metal pipe would be reduced, in particular with almost vertical irradiation.

The shielding device extends at least partially into the annular space section between the glass metal transition element and the connection element. The heat of the first annular disc-shaped portion is thereby better distributed and directed into the cooler region of the annulus section.

It is therefore preferred that the first annular disc-shaped portion merges at its radially outer edge into a first tubular portion which extends into the annular space portion. The tubular portion is preferably cylindrical or conical.

The conical design has the advantage that a good contact with the tubular portion of the connecting element for the purpose of heat conduction can be produced without requiring highly accurate manufacturing tolerances for the connecting element and the tubular portion of the shielding device.

The shielding device preferably has a second annular disk-shaped section. This second annular portion adjoins the first tubular portion and also contributes to better heat distribution.

The second annular disk-shaped section preferably bears against the glass metal transition element or on an annular disk-shaped section of the connecting element. This has the advantage that the shielding means can be fixed by means of the second annular disc-shaped portion. Also, heat can be dissipated via this second annular section to the glass metal transition element or to the connection element and thus be delivered to the surroundings of the absorber tube.

The glass metal transition element preferably has an annular step on which the second annular disk-shaped section of the shielding device is supported.

The second annular disc-shaped portion extends radially outwardly in the annular space formed between the expansion compensation device and the glass metal transition element and, according to one embodiment, can be supported on the glass metal transition element. As a result, an annular chamber which can serve to receive getter material is separated between the second annular disk-shaped section and an outer annular disk-shaped section of the connecting element.

Another embodiment provides that the second annular disk-shaped portion of the shielding device abuts against the annular disk-shaped portion of the connecting element. This embodiment has the advantage that the heat of the shielding device can be dissipated to the outside via the annular disk-shaped section of the connecting element. Depending on the choice of embodiment, the second tubular portion of the shielding device is formed longer or shorter.

The ring stage of the glass-metal transition element also leads to an increase in the diameter of the glass metal transition element in the direction of the pipe end. The annular space between the second annular disk-shaped section and the annular disk-shaped section of the connecting element is thereby increased, so that more space is available for receiving getter material. In addition, the ring stage prevents axial displacement of the shielding away from the end face of the expansion compensation device.

Preferably, the first tubular portion is arranged at a distance from the connection element. In particular, the first tubular portion is arranged at a distance from the tubular portion of the connection element. Thereby, the annular space portion between the glass metal transition element and the connection element is reduced. The area of the first annular disk-shaped section can thereby be increased, so that less radiation can reach the glass-metal transition element from below.

Preferably, the first tubular portion contacts the connection element, preferably the tubular portion of the connection element. This positive contact has the advantage that the heat of the shielding can be derived even better.

Preferably, a getter is disposed in the annulus portion between which the glass transition metal element. A getter is made of a material that is capable of chemically or physically binding residual gases in a largely evacuated space. Thus, the vacuum required for heat insulation of the receiver is maintained in the annulus between the metal tube and the cladding tube over a long period of operation.

The attachment of the getter in the annulus has the advantage that an additional holding device for receiving the getter deleted. The getter is held by the ring portion of the connecting element on the one hand and by the annular disk-shaped portion of the shielding element.

Preferably, the first annular portion extends to an annulus portion between the expansion compensator and the metal tube. This ensures that no heat radiation from the metal tube can strike the end face of the expansion compensation device.

Preferably, the shielding means comprises a second tubular portion extending into this annulus portion. This section has the advantage that the bellows is protected against radiation from the metal tube. This second tubular section also has the advantage that the losses at the pipe end can be minimized by the shield because the radiation of the metal pipe is reflected back.

The shielding device preferably has openings. These openings, which may be holes or slots, are preferably arranged in the second annular disk-shaped section and / or in the first tubular section of the shielding device. Thus in the annulus diffused gases, especially hydrogen, bound by the getter can be, it is advantageous if the gas exchange can take place through these openings.

The shielding device is preferably an annular element. The element is preferably formed as a closed ring. The annular element has the advantage that the mounting position with respect to the rotation about the longitudinal axis of the absorber tube can be chosen arbitrarily.

Preferably, an outer protective cap is provided on the outside of the cladding tube, which covers at least the glass transition element. The permanently mounted outer protective cap protects the glass metal transition element against mechanical damage during the last steps of the production of the absorber tube, during transport and during the assembly process in the power plant. Furthermore, the outer cap protects the glass metal transition element from radiation coming from the outside of the primary mirror. In addition, heat is derived from the glass transition metal element, led to the outside and discharged by convection to the surrounding air.

Exemplary embodiments will be explained in more detail with reference to the drawings.

Show it:

1a a longitudinal section through an absorber tube,

1b a cross section through the absorber tube along the line AA,

2a an enlarged view of the detail X from the 1a .

2 B a representation according to the 2a according to a further embodiment,

3 a representation according to the 2a according to a further embodiment,

4 a perspective view of the shielding device according to a first embodiment and

5 a perspective view of a shielding device according to another embodiment.

In the 1a is an absorber tube 1 shown with longitudinal axis L, which is a metal tube 2 through which a heat exchange fluid flows. Coaxial to the metal tube 2 is a glass tube 4 arranged on both sides via a respective glass metal transition element 10 , a connection element 30 and a strain compensation device 20 in the form of a bellows and a fastener 40 with the metal pipe 2 connected is. In this arrangement, the bellows is located below the connection element 30 and limited to the connection element 30 an outwardly open outer annulus 15 , Between the glass tube 4 and the metal tube 2 becomes an inner annulus 6 formed, which is evacuated or filled with a noble gas.

At the ends 1a , b of the absorber tube 1 the annulus goes 6 in the two annulus sections 7 and 8th above. The annulus section 7 becomes substantially between the glass transition metal element 10 and the connection element 30 educated. The annulus section 8th is located between the metal tube 2 and the expansion compensation device 20 ,

The metal pipe 2 usually has a coating (not shown), which through the glass tube 4 incident solar radiation absorbed optimally. The 1 shows at both ends 1a , b of the absorber tube 1 a strain compensation device 20 , It is also possible the absorber tube 1 only at one end 5a or 5b with such a strain compensation device 20 to provide.

In the 1a is a first embodiment of a shielding device 50 presented in detail in connection with the 2a is described.

In the 1b is a section through the absorber tube 1 along the line AA in 1a shown, wherein the shielding 50 and the outer protective cap 70 were omitted. The axial plan view in the direction of the pipe end 1b on the connection element 30 and the expansion compensation device 20 defines the face 110 having a width B. The section 36 the connection device 30 and the section 26 the expansion compensation device 20 are at the junction 102 connected with each other. The end faces of the sections 26 . 36 form the connection area 100 ,

In the 2a is an enlarged view of the detail X from the 1 shown. The bellows of the expansion compensation device 20 is at the outer end 24 on the fastener 40 attached, in turn, to the metal tube 2 attached, in particular welded. At the inner end 22 the bellows has a connecting portion 26 on which the connection element 30 with its attachment section 36 is attached.

The connection element 30 has a conically shaped tubular portion 34 on top of the annulus section 7 limited and am Pipe end in a ring disk section 32 passes. The ring disk section 32 has an inwardly facing bead 37 and a radially outwardly extending attachment portion 33 , At the attachment section 33 is the glass transition metal element 10 arranged as well as the outer protective cap 70 extending over the entire glass transition element to beyond the end 5b of the glass tube 4 extends. The glass metal transition element 10 has an annular step 12 on, at which the shielding device 50 supported.

The outer protective cap 70 is preferably together with the glass transition metal element 10 and the ring disk section 32 welded in the manufacture of the absorber tube or firmly connected by means of another positive, non-positive or cohesive connection. In this respect, the outer protective cap during subsequent transport serves as additional protection of the glass-metal transition region, namely the connection point between the glass cladding tube 4 and the glass transition metal element 10 ,

The shielding device 50 has a first annular disc-shaped portion 52 on, which is spaced in front of the end face 110 is arranged and the connection area 100 of the attachment section 36 of the connection element 30 and the connection section 26 the bellows 20 covers.

The connection area 100 is without shielding device 50 both the incident and the metal tube 2 exposed to reflected radiation and thus experiences a high thermal load. For leaks in the connection area 100 the negative pressure in the annulus deteriorates 6 , Through the shielding 50 and in particular by the first annular disc-shaped portion 52 is the life of the absorber tube 1 clearly increased.

In the 2a you can see that the first ring-shaped section 52 at an angle α ~ 10 ° with respect to the vertical S on the longitudinal axis L of the absorber tube 1 is arranged inclined. The slope of the section 52 is chosen such that the radially outer edge 53a continue into the annulus 6 protrudes into it as the radially inner edge 53b , The inclined formed first annular portion 52 reflects obliquely incident radiation S1 back to the metal tube 2 , Slanted on the metal tube 2 impinging radiation S2 and S3 is applied to the first annular disk-shaped section 52 reflects the radiation from the connection area 100 , from the bellows 20 as well as the glass transition metal element 10 keeps. The first ring-shaped section 52 thus forms a conical section of the shielding 50 , The shielding device 50 does not contact the bellows.

In the embodiment shown here connects to the outer end 53a a first tubular section 54 on, in a second annular disc-shaped section 56 passes.

The tubular section 34 of the connection element 30 is the same as the first tubular section 54 conical. In the embodiment illustrated here, the first tubular portion is located 54 on the conical section 34 on. The heat of the first tubular section 54 is via the connection element 30 released into the ambient air. The section 54 extends only partially into the annulus section 7 , Wherein approximately the middle of the longitudinal extent of the annular space portion 7 the second annular disc-shaped section 56 connects to an annular shoulder 12 of the glass transition metal element 10 is on. This will make the annulus section 7 in the annulus section 7a and the annular chamber 7b divided.

The glass metal transition element 10 is on one side of the glass tube 4 attached and extends in the axial direction outward, where at the other end of the glass metal transition element 10 with the connection element 30 connected is. The ring shoulder 12 leads to an increase in diameter, causing the annular chamber 7 is extended, leaving ample space for the accommodation of a getter 9 is created (s. 2 B ). The getter 9 is from the annular disc section 32 , the here preferably a inward facing bead 37 and the second annular portion 56 the shielding device 50 held against displacement in the axial direction.

The first ring-shaped section 52 extends radially in the direction of the metal tube 2 where between the expansion compensator 20 and the metal tube 2 another annulus section 8th is formed. The first ring-shaped section 52 covers the entire face 110 from. The section 52 goes into a second tubular section 58 over, located in this annulus section 18 almost to the fastener 40 extends, so that the bellows not only on the end face but also on its underside in front of reflected and emitted radiation of the metal tube 2 is protected.

In the 2 B a second embodiment is shown, which differs from the first embodiment in that the first tubular portion 54 not on the conical section 34 of the connection element 30 rests, creating an annular space section 7c is created. The surface of the first annular disc-shaped section 52 is thereby increased, so that more radiation S ₂ and S ₃ in particular from the glass-metal transition element 10 can be kept away.

In the 3 a further embodiment is shown, which differs from the in 2a described embodiment characterized in that the first tubular portion 54 to the ring disk section 32 of the connection element 30 extends and there in the area of the bead 37 once again. In this case, the getter 9 through the annular disc section 32 and the ring step 12 of the glass transition metal element 10 held. In addition, this embodiment differs in that no section 58 at the shielding device 50 is provided and that the annulus section 7 is not divided. The outer protective cap 70 is outside on the attachment section 33 to the bead 37 pulled in and fastened there.

In the 4 is a perspective view of the shielding 50 to see the embodiment according to the 2 B shows. So that residual gases in the evacuated annulus 6 to the getter 9 are both in the section 54 as well as in the section 56 openings 60 introduced in the form of holes.

In the 5 another embodiment is shown, which instead of holes openings 60 has in the form of radial slots.

In the described embodiments, the shielding device 50 designed as a one-piece element.

LIST OF REFERENCE NUMBERS

1

absorber tube

1a, b

End of the absorber tube

2

metal pipe

4

Glass cladding tube

5a, b

End of the cladding tube

6

inner annulus

7, 7a, c

inner annulus section

7b

annular chamber

8th

Annular section

9

getter

10

Glass metal transition element

12

annular step

15

outer annulus

20

Expansion compensating means

22

inner end

24

outer end

26

connecting portion

30

connecting element

32

Washer section

33

radially outwardly extending mounting portion

34

tubular section

36

radially inwardly extending mounting portion

37

Beading

40

fastener

50

shielding

52

first annular disc-shaped section

53a

radially outer edge

53b

radially inward edge

54

first tubular section

56

second annular disk-shaped section

58

second tubular section

60

opening

70

Outside cap

100

Connection area of connection element and expansion compensation device

102

junction

110

face

B

Width of the annular end face

S

vertical

S ₁

radiation arrow

S ₂

radiation arrow

S ₃

Radiation arrow Inclination angle of the first annular disc-shaped section

Claims (18)

Absorber tube ( 1 ) with a central metal tube ( 2 ) and with a central metal tube ( 2 ) surrounded glass tube ( 4 ), whereby at least one end ( 5a , b) the glass tube ( 4 ) a glass-metal transition element ( 10 ), wherein the metal tube ( 2 ) and the glass-metal transition element ( 10 ) by means of at least one expansion compensation device ( 20 ) are displaceable in the longitudinal direction relative to one another and connected to one another, wherein the expansion compensation device ( 20 ) at least partially in an annulus ( 6 ) between the metal tube ( 2 ) and the glass-metal transition element ( 10 ), wherein an inner end ( 22 ) of the expansion compensation device ( 20 ) on a connecting element ( 30 ), which is connected to the glass-metal transition element ( 10 ) and an outer end ( 24 ) of the expansion compensation device ( 20 ) on the metal tube ( 2 ), wherein between the glass-metal transition element ( 10 ) and the connection element ( 30 ) an annulus section ( 7 ) of the annulus ( 6 ) is formed, and wherein the connecting element ( 30 ) and the expansion compensation device ( 20 ) in axial plan view of an annular end face ( 110 ), characterized in that at least one end ( 1a , b) the absorber tube ( 1 ) in the annulus ( 6 ) at least one shielding device ( 50 ) is arranged, which has a first annular disc-shaped portion ( 52 ), which is spaced in the axial direction in front of the end face ( 110 ) and at least the connection area ( 100 ) from Connection element ( 30 ) and inner end ( 22 ) of the expansion compensation device ( 20 ) covers. Absorber tube according to claim 1, characterized in that the first annular disc-shaped section ( 52 ) with respect to a vertical S on a longitudinal axis L of the absorber tube ( 1 ) is inclined by an angle α ≥ 0. Absorber tube according to claim 2, characterized in that the first annular disc-shaped portion ( 52 ) is arranged inclined so that a radially outer edge ( 53a ) axially further into the room ( 6 ) protrudes as a radially inner edge ( 53b ) of the first annular disc-shaped portion ( 52 ). Absorber tube according to one of claims 2 or 3, characterized in that the angle α is in the range of 0 ° -30 °. Absorber tube according to one of claims 1 to 4, characterized in that the shielding device ( 50 ) at least partially into the annular space section ( 7 ). Absorber tube according to one of claims 1 to 5, characterized in that the first annular disc-shaped portion ( 52 ) at its radially outer edge ( 53a ) into a first tubular section ( 54 ) merges into the annulus ( 7 ). Absorber tube according to claim 6, characterized in that the first tubular section ( 54 ) is cylindrical or conical. Absorber tube according to one of claims 1 to 7, characterized in that the shielding device ( 50 ) a second annular disc-shaped portion ( 56 ) having. Absorber tube according to claim 8, characterized in that the second annular disc-shaped portion ( 56 ) on the glass-metal transition element ( 10 ) or on an annular disk section ( 32 ) of the connecting element ( 30 ) is present. Absorber tube according to one of claims 8 or 9, characterized in that the glass-metal transition element ( 10 ) an annular step ( 12 ), at which the second annular disc-shaped portion ( 56 ) of the shielding device ( 50 ) is supported. Absorber tube according to one of claims 1 to 10, characterized in that the second annular disc-shaped portion ( 56 ) of the shielding device ( 50 ) from the annulus section ( 7 ) an annular chamber ( 7b ) separated between the second annular disc-shaped portion ( 56 ) and a ring-shaped portion ( 32 ) of the connecting element ( 30 ) is arranged. Absorber tube according to claim 11, characterized in that in the annular space section ( 7 ) a getter ( 9 ) is arranged. Absorber tube according to one of claims 1 to 12, characterized in that the first tubular portion ( 54 ) at a distance to the connecting element ( 30 ) is arranged. Absorber tube according to one of claims 1 to 12, characterized in that the first tubular portion ( 54 ) the connecting element ( 30 ) contacted. Absorber tube according to one of claims 1 to 14, characterized in that the first annular disc-shaped portion ( 52 ) of the shielding device ( 50 ) to an annulus section ( 8th ) between the expansion compensation device ( 20 ) and the metal tube ( 2 ). Absorber tube according to claim 15, characterized in that the shielding device ( 50 ) a second tubular section ( 58 ), which at least partially into the annular space section ( 8th ). Absorber tube according to one of claims 1 to 16, characterized in that the shielding device ( 50 ) Openings ( 60 ) having. Absorber tube according to one of claims 1 to 17, characterized in that on the outside of the cladding tube ( 4 ) an outer protective cap ( 70 ) is provided which at least the glass metal transition element ( 10 ) covers.

Images